Coupler, 5 mm to 1/4 inch, for Printrbot Simple All-Metal Z-Axis

Designed this coupler for my broken Z-Axis coupler. The 5 mm hole is suitable for NEMA 17 stepper motor shaft and the 1/4 inch is for the ACME threaded rod.

Now Version 1.1 includes some minor tweaks such as:
1) A middle notch to improve the clamp flexibility.
2) M3 hex nut cutouts to make tightening the clamps convenient and easy.
3) A dimple on the 5 mm hole for steppers with flattened shafts. (Note: as requested, couplerV1-1_forRoundShaft.stl is for non flattened shafts)

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